Metaphit, a proposed phencyclidine (PCP) antagonist, prevents PCP-induced locomotor behavior through mechanisms unrelated to specific blockade of PCP receptors

Abstract

Metaphit, a derivative of phencyclidine (PCP) which irreversibly binds to a population of PCP receptor sites in rat brain, has been considered as a potentially specific PCP antagonist. In whole animal studies, however, metaphit has been shown to have either antagonist or PCP-like actions depending upon the animal species used and the experimental variable evaluated. In the present study, the ability of PCP to produce hyperactivity was assessed in rats following pretreatment with intravenous, intraventricular or intracerebral injections of metaphit. Whereas, intravenous and intraventricular metaphit pretreatment failed to alter the locomotor stimulatory effects of PCP, direct injections of metaphit into the nucleus accumbens resulted in a dose-dependent reduction of PCP-induced hyperactivity. This result also was mimicked by intra-accumbens injections of equimolar concentrations of PCP, but not by the local anesthetic procaine. Additionally, intra-accumbens metaphit prevented d-amphetamine-induced hyperactivity and also depleted significantly accumbens dopamine content; effects not seen after intracerebral PCP administration. These results suggest that metaphit produces a functional antagonism of PCP-induced locomotor activity through presynaptic mechanisms unrelated to specific blockade of PCP receptors.